Fish caught near wastewater treatment plants serving five major U.S. cities had residues of pharmaceuticals in them, including medicines used to treat high cholesterol, allergies, high blood pressure, bipolar disorder and depression, researchers reported Wednesday.

Findings from this first nationwide study of human drugs in fish tissue have prompted the Environmental Protection Agency to significantly expand similar ongoing research to more than 150 different locations.

"The average person hopefully will see this type of a study and see the importance of us thinking about water that we use every day, where does it come from, where does it go to? We need to understand this is a limited resource and we need to learn a lot more about our impacts on it," said study co-author Bryan Brooks, a Baylor University researcher and professor who has published more than a dozen studies related to pharmaceuticals in the environment.

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A person would have to eat hundreds of thousands of fish dinners to get even a single therapeutic dose, Brooks said. But researchers including Brooks have found that even extremely diluted concentrations of pharmaceutical residues can harm fish, frogs and other aquatic species because of their constant exposure to contaminated water.